The Influence of Waterberry on the Development and Composition of Thompson Seedless Grapes

¹ Department of Viticulture and Enology, University of California, Davis, CA 95616.

Rates of post-veraison fruit expansion and sugar accumulation were slower in waterberries than in normally developing grapes (Vitis vinifera L. cv. Thompson Seedless). Titratable acidity was higher in affected fruit and was correlated with a higher concentration of tartaric acid. Malic acid did not contribute significantly to the differences in titratable acidity; both the pattern of malic acid metabolism and its concentration at harvest were similar in waterberries and controls. Respiration rates were also similar in the two types of fruit when measured as oxygen uptake. However, the respiratory quotient of controls rose to 1.8 after veraison, while the RQ of waterberries remained below 1.0, suggesting differences in respiratory substrate. Potassium accumulation, which was rapid in control fruit, was much slower in waterberries. Conversely, although calcium accumulation slowed in controls after veraison, it remained rapid in waterberries. The dissimilar patterns of calcium and potassium accumulation suggest differences in the balance between phloem and xylem transport in waterberries and in normally developing grapes after veraison.

Key words: Thompson Seedless vines, waterberry

Submitted on March 1, 1990